The present invention relates to a lightning arrestor device of the type used in particular for ensuring protection of high power electric installations.
It is known that, in order to ensure protection of such installations against lightning, lightning arrestor devices are employed which are connected between a mains wire and earth, and which comprise components which, in normal functioning, behave like neutral elements but which, in the event of violent excess voltages, become conducting, so that they deviate the current due to the lightning towards earth, thus protecting the installation disposed downstream against the destructive effects of the excess voltage.
As a safety measure standard IEC 61643-1 renders it compulsory to associate with the lightning arrestor a disconnector whose role is to cut the circuit if the lightning arrestor is destroyed. Such disconnectors may be essentially disposed in two configurations.
In a first configuration, the disconnector is disposed, as shown in FIG. 1, on the line itself. Under these conditions, it will be understood that its disconnection brings about cut of electrical power of the installations located downstream.
In the second configuration, shown in FIG. 2, the disconnector is disposed on the by-pass branch going to earth, so that its disconnection indeed respects a continuity of service since the current can continue to circulate in the principal branch, but it no longer ensures a continuity of the protection since it interrupts the by-pass towards earth.
It will be understood that neither of these two configurations is totally satisfactory, since, after destruction of the lightning arrestor and the activation of the disconnector which is associated therewith, the first has the effect of paralyzing the installation and the second has the effect of placing the latter in danger.
It is also known that another quality of a lightning arrestor is its capacity to allow the excess voltages to pass without any wear occurring. This is why it appears advantageous to constitute such a lightning arrestor from elements which are particularly resistant to wear and tear such as semi-conductor junctions of Zener type which, furthermore, present other qualities with respect to the other lightning arrestor devices of the prior state of the art, such as in particular dischargers and varistors.
DE-4124321-A describes a device for protection against excess voltages, comprising components with variable resistance as a function of the voltage, such as varistors, connected respectively in series with disconnectors, such as fuses, in at least two circuit branches extending in parallel between an electrical power line having to be protected against excess voltages and earth.
The present invention has for its object to overcome the drawbacks mentioned above by proposing means for protection against the effects of lightning which ensure, after a lightning stroke, both the continuity of service for the installation and its protection against a subsequent lightning stroke, and this with components of Zener type.
The present invention thus has for its object a lightning arrestor device for protecting an installation powered by an electric transmission line, consisting of at least two assemblies connected in parallel between the line terminals and each comprising a disconnector mounted in series with at least one voltage-dependent variable resistance component, characterized in that the variable resistance component is a Zener diode, at least one assembly consisting of at least two Zener diodes arranged in parallel.
According to the invention, the threshold voltages of the respective Zener type diodes of said assemblies will preferably be adjacent.
In an embodiment of the invention, one of the assemblies comprises a Zener type diode of which the threshold voltage is greater than that of the Zener diodes of the other assemblies.
The threshold voltage of said assembly is preferably greater than the threshold voltage of the other assembly by a value equal to substantially the voltage difference between the low current and high current values of the other assembly.
As will be set forth hereinbelow, such a differentiation of these diodes makes it possible to avoid, in cases of very particular characteristics of excess voltages due to lightning, that the two Zener diodes simultaneously become conducting and be destroyed, in that case leaving the installation bereft of protection.
In order to make a selection, it is also possible to give one of the assemblies short links and the other assembly long links.
In a preferred embodiment of the invention, at least one of the assemblies constituted by at least two Zener diodes in parallel presents electrical links between these diodes and the installation which are shorter links than those of the other assemblies.